1. Field of the Invention
The present invention relates to a method for characterizing pixels of an image sensor and, more specifically, to a method for measuring the crosstalk between adjacent pixels, adapted to any type of image sensor pixels.
2. Discussion of Related Art
In an integrated image sensor, elementary photodetection cells, called pixels, are formed at the surface of a semiconductor substrate. Each pixel generally comprises an area where photogenerated charges are collected and elements for transferring these charges to an electronic circuit capable of processing this information.
The pixels of the pixel array are isolated from one another to limit as much as possible the capture by a neighboring pixel of photons or photogenerated charges intended for a given pixel (crosstalk).
When a new image sensor pixel structure is designed, a characterization of the sensor pixels is necessary to determine whether the operation of the new pixels is improved with respect to that of known pixels or to characterize other parameters of these pixels (dark currents, noise, saturation). It is generally provided to characterize the crosstalk between pixels.
Several techniques are known to perform such a characterization. It has, in particular, been provided to illuminate the device by means of a thin local beam capable of lighting a single pixel of the image sensor. The number of electrons detected by the pixels adjacent to the illuminated pixel is then measured. This enables to know the leakage of photogenerated charges from one pixel to the surrounding pixels, in all directions. This measurement is performed for several wavelengths, and for pixels topped with color filters of different colors.
However, the method cannot work when the pixel size becomes very small. Indeed, in this case, the illumination of a single pixel becomes difficult, or even impossible, and cannot be performed without causing diffraction phenomena which prevent a proper characterization of the pixels.
A method for characterizing an image sensor pixel compatible with small pixels and representative of the normal operation of this pixel is thus needed.